The present invention relates to a piezoelectric/electrostrictive element driving circuit which is used for actuators, transducers, various vibrators, micro-machines and the like.
In actuators, transducers, various vibrators and micro-machines which are driven by piezoelectric elements or electrostrictive elements (piezoelectric/electrostrictive element), for example, the piezoelectric/electrostrictive element is charged and discharged to be deformed, and shifts and movements are made possible by utilizing this deformation. In such a driving circuit, where the piezoelectric/electrostrictive element is charged and discharged, if discharging electric charges are discharged as Joule heat by resistance or the like, the power consumption becomes large and the calorific value becomes large. For this reason, the discharging electric charges are prevented from being discharged as heat as much as possible, and they are recovered to be utilized as the next charging power, and the power consumption is reduced.
For example, in Japanese Patent No. 2909150, a plurality of piezoelectric elements are actuated at different times so that the discharging electric charges of the piezoelectric elements are directly used for charging other piezoelectric elements. As a result, energy which is consumed as heat by exchanging the electric charges between the piezoelectric elements is reduced. Moreover, Japanese Patent Application Laid-Open No. 10-107335 (1998) discloses a circuit in which a capacitor used exclusively for the recovery of charging electric charges is provided, and some discharging electric charges of the piezoelectric elements are stored in this capacitor to be utilized for next charging. Further, this circuit is configured so that a coil is provided in a charging/discharging circuit, and the recovered electric charge amount and reused electric charge amount are increased by LC resonance.
However, where a plurality of piezoelectric elements are provided and electric charges are exchanged between the piezoelectric elements, the power recovery efficiency is 50% at most. Where the capacitor exclusively for the recovery of electric charges is provided, when a coil is provided, the power recovery efficiency can be raised to about 90% maximally, but since this circuit requires an external capacitor, it is not suitable for miniaturization. Moreover, if both the structures are combined, a structure in which a coil is provided to the circuit where the electric charges are exchanged between the piezoelectric elements is obtained. However, with this structure, the charging/discharging timing between the piezoelectric elements is restricted, and it is difficult to optimize the charging/discharging waveform.
The present invention has been devised from the above viewpoint. It is an object of the present invention to provide a piezoelectric element driving circuit in which power recovery efficiency is high, power consumption is small, the degree of freedom of charging/discharging timing is high, and external elements (such as a capacitor for recovering a power) are not required.
In order to solve the above problem, a first aspect of the invention provides a piezoelectric/electrostrictive element driving circuit, characterized by including piezoelectric/electrostrictive elements which operate alternatively, a plurality of steps of charging circuits for charging the piezoelectric/electrostrictive elements, and a plurality steps of discharging circuits for discharging the piezoelectric/electrostrictive elements. At least the first-step charging circuit of the charging circuits and discharging circuits is connected with a resistance/resistances and a coil/coils in series with the piezoelectric/electrostrictive elements, and serves as the first-step discharging circuit of the other piezoelectric/electrostrictive elements mutually, and the discharging electrical charges on one side can be used directly as charging electrical charges on the other side.